1. Field of the Invention
The disclosed invention generally relates to a thermal bonding method. More particularly, the disclosed invention relates to a thermal bonding method usable to effectively bond plastic tubular structures to one another such as, for example, balloon type structures to catheters.
2. Description of the Prior Art
Medical balloon structures are typically assembled in combination with basal tubular structures such that the balloon is the outer component. The balloon is typically thin and thermal energy needs to be applied from the outside inward. To thermally bond a balloon to a basal tubular structure, thermal energy must first transfer through the balloon in the neck area. To join two materials, especially if they are not the very same material of the same compound and hardness, both materials must be brought close to their melt point or to their softening point so that the materials will fuse together or “mix” together at the skin level. Just melting the “top” material and making contact with the material underneath often will not provide the secure bond and complete fusion required. Since the outer component is heated first it actually has to get hotter than is needed at the joining area, which is the inside wall of the outer component and the outer wall of the inside component. The inner component or tube immediately acts as a heat sink absorbing heat and taking it away from the joint area. The shaft is often of a higher hardness than the balloon and can have a higher melt point. This means that the outer material may need to be heated beyond its own melting point to obtain a proper bond.
In structural situations characterized by a shaft or basal tubular structure and balloon comprising two different materials, which can also be of different hardnesses, the melt points can be much different. Normally it is assumed the shaft will have the higher melt point, which increases the difficulty of thermal bonding. When the balloon would have the higher melting point then the problem still exists but in reverse. To get the balloon neck surface to its melting point can deform, degrade or destroy the shaft at the joining area. In some cases the two materials being used have been found to be non bondable by existing thermal means. In other words even when softened by heat or slightly melted the two materials do not mix well and will not join, one to the other. Balloon, or shaft, materials, such as PET, that are semi-crystalline and do not soften when heated and can not be thermally bonded using traditional methods.